Patent GB-1356924-A (GB)
Title: Electric motors
IPC: H02K5/128
Filed: 1970-06-30
Abstract: 1356924 Control of A.C. motors A J WALKER 29 June 1971 [30 June 1970] 31479/70 Headings H2A and H2J An electric motor comprises an armature co-operating with a stator having two or more poles, independently operated and controllable commutating means connected to a supply and to the stator windings to produce a rotating magnetic field in the stator, a further armature drivably coupled to the commutating means and co-operating with the stator, urged to rotate thereby when the commutating means is connected to the supply, which rotation is independent of the rotation of the armature, and speed control means for the further armature. The motor is particularly suited for driving a pump with which it may form an integral unit. In Fig. 1, the stator 20 has three poles 20A each provided with an energizing winding 22, the armature 11 rotates about a fixed spindle 12 and carries a permanent ring magnet 25 and the supply for windings 22 is provided via brushes 7, 7A, slip-rings 6, 6A, brushes 8 and commutator segments 4A, 4B, 4C arranged in three groups as shown in Fig. 3, with corresponding connections to the windings 22 to form a star or delta arrangement. The armature 11 is integral with the blades 13 of a pump and is separated from the stator 20 by a non-magnetic fluidretaining shell 21 whose periphery is secured to the pump casing 40, the stator casing 14 and a fluid-tight sealing gasket 44. Members 6, 6A and 8 are carried by a brush-holder 5 driven by a further armature 27 which is integral therewith and is arranged within an extension of the stator 20 to be rotated by its magnetic field. Armature 27 comprises a permanent ring magnet or a ring of low electrical resistivity in which eddy currents are induced. The speed of the brush-holder 5 may be varied by friction pad braking (not shown) or by an eddy current brake comprising a low resistance ring 23 attached to the holder 5 and a magnet 29 adjustable in relation to the ring 23. Alternatively the speed variation may be achieved as shown in Fig. 2, by using an armature 27 having two poles 27B whose energizing windings 27A are connected to a supply via an additional brush and slip-ring 7B, 6B, the combination 6, 7 and a rheostat VR adjustable to vary the current in the windings 27A. The brushholder may have inclined slots arranged so that the members 6, 8 may be replaced by a single brush which engages the segments connected to the stator and slip rings connected to the supply, Fig. 4 (not shown). In a modification, Figs. 5 and 6 (not shown), the commutator comprises a hermetically sealed housing (72) containing mercury (71) and fixed contacts (70A ... 70D) connected to the stator windings, the mercury being rotated as a ring by a disc (73) which has a wave producing member (74) to effect contact between the mercury and the contacts and which carries a magnet (78A) magnetically coupled with a magnet (78B) carried by a shaft (79). Alternatively, two housings insulated from one another may be used, with the two discs mechanically connected. When the armature 11 is of the permanent magnet type, the stator supply is D.C. or A.C. rectified by rectifiers incorporated in the brush-holder. If the armature 11 is of the squirrel-cage type the stator supply is A.C. The invention may be applied to linear motors or to motors wherein the pole surfaces define a surface of revolution.